The main factors affecting population size were investigated in a population of Heteronotia binoei the general biology of which was already well known. Population size fell by about 40% during a two year observation period and this appeared to have been due to adverse climatic effects greatly depressing egg incubation success. The effect of this was soon apparent as H. binoei is a short-lived species.

An upper limit to population size appears to be set by social behaviour (territoriality) acting in conjunction with the available home-sites. When population size is large the effects of this are buffered to some degree by overspill into an inferior home-site.